1. Technical Field
The present invention is related to a method for synchronizing signals, and more particularly, to a method for synchronizing a display horizontal synchronization signal to an external horizontal synchronization signal and devices thereof.
2. Description of the Prior Art
DisplayPort, a standard announced by the Video Electronics Standards Association (VESA), simplifies display design and connections. DisplayPort possesses stable electrical characteristics, hence providing higher resolution support.
A number of companion standards have developed according to DisplayPort, for providing optimization to different applications. For instance, internal DisplayPort (iDP) targets digital TV systems and high-end display devices, Embedded DisplayPort (eDP) standard targets embedded display devices (e.g. laptop displays, etc.), and Mini DisplayPort (mDP) standard is for miniaturized connectors. Taking the Embedded DisplayPort standard as an example, a laptop can output signals from a processing unit (e.g. a graphics processing unit) to control the display panel directly, for reducing components and wiring required between the monitor and the motherboard. This way, weight and power consumption of the laptop can be reduced, and product appearance can be more streamlined.
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a conventional portable device 100 comprising a DisplayPort interface. The portable device 100 comprises a processing unit 110 and a display device 120. The processing unit 110 comprises a transmitting end Tx, and can be a central processing unit (CPU) or a graphics processing unit (GPU), etc. The display device 120 comprises a receiving end Rx, buffer memory M and a timing controller TCON. The transmitting end Tx and the receiving end Rx are both compliant to DisplayPort interface. The transmitting end Tx of the processing unit 110 is coupled to the receiving end Rx of the display device 120 via a unilateral Main Link (ML) and a bilateral Auxiliary Link (AL). The buffer memory M stores, for instance, data of a static image.
The DisplayPort interface comprises Panel Self-Refresh (PSR) technology. When a user operates the portable device 100, the processing unit 110 transmits a driving signal to the display device 120. The timing controller TCON drives the display device 120 according to the driving signal transmitted by the processing unit 110. When the portable device 100 is idle for a predetermined duration, the processing unit 110 stops transmitting the driving signal to the display device 120. The timing controller TCON then self-generates the driving signal to drive the display device 120 for displaying the static image stored in the buffer memory M. This way, the Panel Self-Refresh technology can further reduce the power consumption of the portable device 100 when the portable device 100 is idle.
When the portable device 100 is operated again in the idle state, the processing unit 110 begins transmitting the driving signal to the display device 120 again. However, time sequence and phase of the driving signal generated by the processing unit 110 may be different from those of the driving signal generated by the timing controller TCON. The timing controller TCON is required to be synchronized with the processing unit 110 for the timing controller TCON to drive the display device 120 according to the driving signal transmitted by the processing unit 110 again. Generally, the timing controller TCON utilizes a continuous capture method to adjust internal signal timing of the display device 120, which changes a frame rate of the display device 120, so as to synchronize the driving signals generated by the processing unit 110 and the timing controller TCON. To reduce frame loss during synchronization, read/write action of a frame buffer is controlled to synchronize the driving signal generated by the timing controller TCON to the driving signal generated by the processing unit 110. However, synchronizing the internal driving signal generated by the timing controller TCON to the external driving signal generated by the processing unit 110 requires complicated read/write action of the frame buffer, and utilizes extra hardware resources such as a line buffer, etc. Furthermore, substantial frame duration is required to achieve synchronization between the driving signals generated by the timing controller TCON and the processing unit 110, such that the user perceives pauses in screen display of the display device 120, causing viewing discomfort.